Self‐Assembled Membranes for High Ion Selectivity and Proton Blocking in Electrochemical Applications

Abstract Anion‐exchange membranes (AEMs) with high anion/cation selectivity and exceptional proton‐blocking ability are critical for applications such as bipolar membrane electrodialysis and electrochemical acid recovery. However, existing AEMs are constrained by a trade‐off between ionic conductivity and selectivity, largely due to the intrinsic coupling between charge density and water content, and they suffer from excessive proton leakage facilitated by the Grotthuss hopping mechanism. In this work, poly(vinylimidazolium) membranes functionalized with long alkyl side chains that self‐assemble into well‐defined microphase‐separated morphologies stabilized by hydrophobic and electrostatic interactions are reported. These unique structures localize the charge density along the polymer backbone to promote fast and selective ion transport. As a result, these membranes exhibit ionic conductivities and counter‐ion diffusivities surpassing those of conventional homogeneous membranes, along with unprecedented counter‐ion/co‐ion selectivity and proton‐blocking ability. These results establish a new design paradigm for high‐performance, phase separated charged polymer membranes that overcome the limitations of homogeneous membranes, with broad implications for advanced electrochemical technologies.